This invention relates to the coating of metal sheet. More particularly, this invention relates to a system for high speed electrophoretic coating of metal sheet stock.
Metal sheet stock such as, for example, aluminum, is conventionally coil coated prior to subsequent fabrication of the metal into desired objects such as containers, siding, or the like, by uncoiling the metal and passing it through cleaning and conversion coating operations prior to application of an organic coating material thereon. While the cleaning and conversion coating may be done at relatively high speeds (1200-1600 feet per minute) conventional organic coatings are then applied at much lower speeds (500-600 feet per minute) because of heat buildup, wear of the rolls, slinging of material from the rolls, as well as curing or drying requirements with such conventional organic materials.
It is known to electrophoretically coat metal on a continuous basis. For example, Rimbach U.S. Pat. No. 2,576,362 illustrates a process wherein a wire is passed through a coating station located above a bath whereby the wire as it is unwound is passed through the station and subsequently through a heating station without any redirecting of the wire around other rollers which would change the direction of the wire to either slow the speed down or interfere in any way with the coating thereon.
It is also known to electrodeposit coating material on coiled metal stock. For example, Clark U.S. Pat. No. 2,214,876 discloses electrocoating of aluminum, tantalum, magnesium, or the like by electrodeposition of an organic coating material onto the metal. Metcalfe et al. U.S. Pat. No. 2,898,279 also shows the electrodeposition of coating materials on sheet which may be metallic. However, in both instances the substrate to be coated is directed into a coating bath via rollers or the like which can slow down the coating line or interfere with the application of the coating to the substrate.
While, as referred to above, it is not unknown to coat a material outside of the bath, such processes are usually limiting in that either the coating station is of short length with a slow passage therethrough (to provide adequate residence time) or a longer coating line s used--to again provide adequate residence time--but necessitating the use of supporting rollers which, in turn, interfere with the coating of the substrate.